The present invention relates to a semiconductor pressure sensor to be used for various purposes such as medical treatment.
A semiconductor pressure sensor is used to measure pressure based on the principle that the resistance value of silicon changes according to the deformation of a silicon diaphragm.
To increase the sensitivity of this pressure sensor, it is better that the silicon diaphragm is thinner. However, because the problem of strength arises when it is too thin, it is normally practiced to cut silicon wafer to the thickness of 0.5-1 mm mechanically or by chemical agent except the supporting part so that the pressure-sensitive portion has a thickness of several microns.
In case it is cut or thinned down mechanically or by chemical agent, it is extremely difficult to accurately control the thickness of the silicon diaphragm because the etching speed varies according to the concentration, temperature, etc. of the etching solution. For this reason, the thickness control by etching has been performed in the past by PN junction or change of the impurity concentration of silicon. Even when pressure sensor is produced by above mentioned methods, the thickness is not controlled satisfactorily. Moreover, this method was disadvantageous because temperature characteristics--especially, high temperature characteristics, are not so good.